The present invention relates to measuring the presence or concentration of an analyte in a sample, particularly by spectrophotometry on a diagnostic analyzer. In particular, the present invention relates to reducing the number of rejects or re-runs in measuring the concentration of an analyte in a sample by taking multiple measurements through the cuvette containing the sample and reagent.
Known diagnostic assays and other analysis that use cuvettes as the reaction chamber or container for taking measurements often have problems with imprecise results associated with measurements of emitted light, such as absorbance measurements, that are influenced by interfering objects in the measurement path. These interfering objects, which can be transient or non-transient, can include any number of things from dirt or dust in the cuvette, dirt or dust on the exterior of the cuvette window, fingerprints on the surface of the cuvettes and air bubbles in the fluid. In addition to interfering objects, measurement error and therefore imprecision of diagnostic assays performed in a cuvette can be influenced by measuring a fluid, e.g., sample, that was not homogeneously mixed (chemically or thermally). The problems of interfering objects can be exacerbated by open top cuvettes which are open to receiving fluids (e.g., sample and/or reagents) from a dispensing or aspirating pipette or proboscis and are thus open to the introduction of dirt from the ambient environment and additional bubbles from the dispense of fluid into the cuvette. The present inventors have found that these transient conditions can be substantial contributors to assay imprecision which often leads to the assay being rejected, thus resulting in the time consuming and costly reanalysis (re-running) of samples. Some of these factors can be reduced by controlling the analysis process. For example, mixing within the cuvette can be improved as disclosed in pending application Ser. No. 10/622,258 filed Jul. 18, 2003 entitled “Improved Fluid Mixing.” Cuvette loading can be improved to reduce dirt and fingerprints as disclosed in pending application Ser. No. 10/684,536 filed Oct. 14, 2003 entitled “Packaging Of Multiple Fluid Receptacles.”
A more difficult problem to eliminate or reduce is the formation of air bubbles in the fluid. The bubbles can be introduced by air being mixed in during sample or reagent dispense. Alternatively, air bubbles can be formed in the fluid because the fluid has more dissolved air present when it is cold than when it is warm, and the reagents, which are stored cold, are warmed up in the cuvettes. As a result, bubbles of air tend to form on the surfaces of the cuvette as the reagents are warmed. If they are located in the measurement window part of the cuvette they may cause substantial error in the measurement and ultimately in the determination of the assay concentration.
U.S. Pat. No. 4,123,173 discloses a rotatable flexible cuvette array. U.S. Pat. No. 4,648,712 discloses a method for determining the basis weight of a fibrous web that includes reading multiple areas of web. U.S. Pat. No. 4,549,809 discloses curved cuvettes and taking multiple readings to determine the position of the cuvette and using a single measurement for analysis. U.S. Pat. No. 5,402,240 discloses a sperm densimeter that takes a plurality of sample transmission measurements and calculates an average based on the plurality of measurements. U.S. Pat. No. 5,535,744 discloses an analysis method that includes multiple reads for each cuvette which are averaged to determine a final result. U.S. Pat. No. 5,255,514 discloses a method for determining wash effectiveness on a dry slide test element that includes reading at different locations on the slide. U.S. Pat. No. 5,853,666 discloses a sealed test card having a plurality of wells containing sample to be analyzed by fluorescence. Measurements are taken at multiple positions across the well to detect any air pockets or debris and to detect and reject abnormal transmittance measurements.
None of the known art described above, adequately addresses resolving the problems described above, in particular, of improving precision of measurements through a cuvette to reduce or even eliminate the number of re-runs that have to be performed on a sample, in particular, by detecting and reducing or eliminating errors in reading through a cuvette. For the foregoing reasons, there is a need for a method of improving precision, more particularly detecting and reducing or eliminating errors during measurement of an analyte by spectrophotometry.